High purity hafnium, target and thin film comprising said high purity hafnium, and method for producing high purity hafnium

ABSTRACT

The present invention relates to high purity hafnium having a purity of 4N or higher excluding zirconium and gas components and an oxygen content of 40 wtppm or less, and a target and thin film formed from such high purity hafnium, and high purity hafnium having a purity of 4N or higher excluding zirconium and gas components and in which the content of sulfur and phosphorus is respectively 10 wtppm or less. The present invention also relates to a high purity hafnium material which uses a hafnium sponge with reduced zirconium as the raw material, and in which the content of oxygen, sulfur and phosphorus containing in the hafnium is reduced, as well as to a target and thin film formed from such material, and to the manufacturing method of high purity hafnium. Thereby provided is efficient and stable manufacturing technology which enables the manufacture of a high purity hafnium material, and a target and thin film formed from such material.

TECHNICAL FIELD

The present invention relates to a high purity hafnium material in whichthe content of impurities such as zirconium, oxygen, sulfur andphosphorus contained in the hafnium is reduced, as well as to a targetand thin film formed from such high purity hafnium material, and amanufacturing method of high purity hafnium.

BACKGROUND ART

Conventionally, there are numerous documents relating to the manufactureof hafnium, and, since hafnium and zirconium are very similar in termsof atomic structure and chemical property, the inclusion of zirconium orthe inclusion of zirconium in hafnium was never really acknowledged as aproblem as exemplified below.

Hafnium and zirconium are superior in heat resistance and corrosionresistance, and are characterized in that they have a strong affinitywith oxygen and nitrogen. And, since the oxides or nitrides thereof havesuperior stability in high temperatures, they are utilized asfire-resistant materials in the manufacture of nuclear ceramics, steelor castings. Further, recently, these are also being used as electronicmaterials or optical materials.

The manufacturing method of metal hafnium or metal zirconium is proposedas the same manufacturing method. As such example, there is a method ofreacting a fluorine-containing zirconium or hafnium compound with metalaluminum or magnesium in inert gas, reducing gas or vacuum at atemperature of 400° C. or higher (e.g., refer to Patent Document 1); amanufacturing method of reducing zirconium chloride, hafnium chloride ortitanium chloride and manufacturing the respective metals thereofcharacterized in the sealing metal (e.g., refer to Patent Document 2); amanufacturing method of hafnium or zirconium characterized in thereaction container structure upon reducing zirconium tetrachloride orhafnium tetrachloride with magnesium and the manufacturing techniquethereof (e.g., refer to Patent Document 3); a method of manufacturingchloro-, bromo- or iodic zirconium, hafnium, tantalum, vanadium andniobium compound vapor by introducing these into a crucible (e.g., referto Patent Document 4); a method of refining zirconium or hafniumchloride or an acid chloride aqueous solution with strongly basic anionexchange resin (e.g., refer to Patent Document 5); a method ofcollecting zirconium via solvent extraction (e.g., refer to PatentDocument 6); and a crystal bar hafnium manufacturing device havingcharacteristics in the feed portion (e.g., refer to Patent Document 7).

[Patent Document 1] Japanese Patent Laid-Open Publication No. S60-17027

[Patent Document 2] Japanese Patent Laid-Open Publication No. S61-279641

[Patent Document 3] Japanese Patent Laid-Open Publication No. S62-103328

[Patent Document 4] WO89/11449

[Patent Document 5] Japanese Patent Laid-Open Publication No. H10-204554

[Patent Document 6] Japanese Patent Laid-Open Publication No. S60-255621

[Patent Document 7] Japanese Patent Laid-Open Publication No. S61-242993

As described in the foregoing documents, although there are numerousrefining methods and extraction methods of zirconium and hafnium, theinclusion of zirconium or the inclusion of zirconium in hafnium wasnever really acknowledged as a problem.

Nevertheless, in recent years, deposition on electronic components usinghafnium silicide is being demanded. In such a case, even zirconium is animpurity, and there is a possibility that the required characteristicsof the hafnium raw material may become unstable. Therefore, there isdemand for a high purity hafnium material with reduced zirconium, and atarget and thin film formed from such a material.

However, since there was no notion of separating hafnium and zirconiumas described above, the actual condition is that there is no efficientand stable manufacturing technology for obtaining the foregoing highpurity hafnium material with reduced zirconium, and a target and thinfilm formed from such a material. Further, since it is difficult toefficiently eliminate the impurities of oxygen, sulfur and phosphorus,this is another reason that high purification has been neglectedheretofore.

In particular, materials having a high residual resistance ratio arebeing demanded, and, since a high purity hafnium material could not beobtained conventionally, it was not possible to sufficiently meet thedemands as electronic component materials since the residual resistanceratio was low.

DISCLOSURE OF THE INVENTION

Thus, an object of the present invention is to provide a high purityhafnium material which uses a hafnium sponge with reduced zirconium asthe raw material, and in which the content of oxygen, sulfur andphosphorus contained in the hafnium is reduced, as well as to a targetand thin film formed from such material, and to the manufacturing methodof high purity hafnium. Thereby provided is efficient and stablemanufacturing technology which enables the manufacture of a high purityhafnium material, and a target and thin film formed from such material.

MEANS FOR SOLVING PROBLEMS

In order to achieve the foregoing object, as a result of intense study,the present inventors discovered that the intended high purity hafniumcan be manufactured by using a hafnium sponge with reduced zirconiumdeveloped previously by the inventors as the raw material, and furtherperforming electron beam melting and deoxidation with molten salt so asto efficiently separate oxygen, sulfur and phosphorus, and, asnecessary, further performing electron beam melting.

Based on the foregoing discovery, the present invention provides:

1) High purity hafnium and a target and thin film formed from the highpurity hafnium having a purity of 4N or higher excluding zirconium andgas components, and an oxygen content of 40 wtppm or less;

2) High purity hafnium and a target and thin film formed from the highpurity hafnium having a purity of 4N or higher excluding zirconium andgas components, and in which the content of sulfur and phosphorus isrespectively 10 wtppm or less;

3) High purity hafnium and a target and thin film formed from the highpurity hafnium according to paragraph 1) above having a purity of 4N orhigher excluding zirconium and gas components, and in which the contentof sulfur and phosphorus is respectively 10 wtppm or less;

4) High purity hafnium and a target and thin film formed from the highpurity hafnium according to any one of paragraphs 1) to 3) above havinga purity of 4N or higher excluding zirconium and gas components, and inwhich the zirconium content is 0.5 wt % or lower;

5) A manufacturing method of high purity hafnium wherein a hafniumsponge raw material is subject to solvent extraction and thereafterdissolved, and the obtained hafnium ingot is further subject todeoxidation with molten salt; and

6) The manufacturing method of high purity hafnium according toparagraph 5) above wherein, after performing deoxidation with moltensalt, electron beam melting is further performed.

[Effect of the Invention]

The present invention yields a superior effect in that it is capable ofstably manufacturing high purity hafnium by using a hafnium sponge inwhich the zirconium in the hafnium is eliminated as the raw material,and further performing electron beam melting and deoxidation with moltensalt to this hafnium sponge. Further, by manufacturing a sputteringtarget with the high purity hafnium ingot obtained as described aboveand performing sputtering with this target, it is possible to obtain ahigh purity hafnium thin film. Moreover, it is possible to obtain a thinfilm having a high residual resistance ratio from the high purityhafnium material, which will be able to sufficiently meet the demands asan electronic component material.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, a hafnium sponge from which zirconium has beeneliminated is used as the raw material. Upon eliminating zirconium fromhafnium, a method invented previously by the present inventors may beadopted, or another raw material may be used so as long as it is hafniumwith reduced zirconium.

The previous invention as a method for reducing zirconium is introducedbelow.

Hafnium tetrachloride (HfCl₄) is used as the raw material. Acommercially available material can be used as the hafniumtetrachloride. This commercially available hafnium tetrachloridecontains roughly 5 wt % of zirconium. Incidentally, hafnium (Hf) metalor hafnium oxide (HfO₂) may also be used as the raw material.

These raw materials have a purity level of 3N excluding zirconium, andcontain iron, chrome and nickel as main impurities other than zirconium.

First, this hafnium tetrachloride raw material is dissolved in purifiedwater. Next, this is subject to multistage organic solvent extraction.Normally, solvent extraction is performed in 1 to 10 stages. TBP may beused as the organic solvent.

As a result, zirconium can be made to be 5000 wtppm or less, and can befurther made to be 1000 wtppm or less by repeating solvent extraction.Further, the total content of other impurities can be made to be 1000wtppm or less.

Next, neutralization treatment is performed to obtain hafnium oxide(HfO₂). This hafnium oxide is subject to chlorination to obtain highpurity hafnium tetrachloride (HfCl₄), and this is further reduced with,for instance, magnesium metal having chloridization power that isstronger than hafnium or zirconium to obtain a hafnium sponge. As thereducing metal, in addition to magnesium, for instance, calcium, sodium,and so on may be used.

In the present invention, the hafnium sponge obtained as described aboveis once subject to electron beam melting (hearth melting) in a Cucrucible. Thereafter, the hafnium sponge is sequentially placed therein.The hafnium molten metal overflowing from the upper part of the poolflows into the upper part of the ingot. This is still in a molten metalstate, and the purity can be improved by performing the two meltingprocesses with a series of electronic beam operations at the stages ofhearth melting and manufacturing the ingot.

Thereafter, the obtained ingot is subject to deoxidation with moltensalt. This deoxidation process, as described later, is able to eliminatecarbon, sulfur, phosphorus and other impurities. Specifically, it ispossible to make oxygen 40 wtppm or less, and sulfur and phosphorusrespectively 10 wtppm or less. In the foregoing process, zirconium canbe made to be 5000 wtppm or less, and further 1000 wtppm.

Like this, it is possible to obtain a high purity hafnium ingot having apurity of 4N (99.99 wt %) or higher excluding gas components such ascarbon, oxygen and nitrogen, and zirconium.

Further, it is possible to use this high purity hafnium to manufacture ahigh purity hafnium target, and it is further possible to deposit highpurity hafnium on a substrate by performing sputtering with this highpurity target.

Moreover, a material having a high residual resistance ratio can beobtained from the foregoing high purity hafnium material as described inthe following Examples, and it is possible to sufficiently meet thedemands as an electronic component material.

The target may be manufactured with the ordinary processing steps offorging, rolling, cutting, finishing (polishing) and so on. There is noparticular limitation in the manufacturing method thereof, and themethod may be selected arbitrarily.

EXAMPLES

Examples of the present invention are now explained. These Examples aremerely illustrative, and the present invention shall in no way belimited thereby. In other words, the present invention shall only belimited by the scope of the present invention, and shall include thevarious modifications other than the Examples of this invention.

Example 1

100 Kg of commercially available hafnium tetrachloride (HfCl₄) shown inTable 1 having a purity of 3N and containing roughly 5000 wtppm ofzirconium was used as the raw material, and this was dissolved in 1 L ofpurified water to create a nitric acid solution.

This raw material contained 500 wtppm, 40 wtppm and 1000 wtppm of iron,chrome and nickel, respectively, as its main impurities in HfCl₄.

Next, this hafnium raw material (a nitric acid solution) was subject to4-stage organic solvent extraction using a TBP organic solvent, andneutralization treatment was performed to obtain hafnium oxide (HfO₂).

Further, this hafnium oxide was subject to chlorination to obtain highpurity hafnium tetrachloride (HfCl₄), and then subject to magnesiumreduction to obtain a hafnium sponge as the raw material. This hafniumsponge contained 300 wtppm of zirconium, and the total content of otherimpurities was reduced to 300 wtppm.

Next, the obtained hafnium sponge was used as the raw material, andfurther subject to two-stage melting via hearth melting and ingotmelting with an electron beam to remove volatile elements, gascomponents and so on. As a result of the foregoing process, although thezirconium content did not change at 300 wtppm, iron, chrome, nickel andother impurities were reduced to 70 wtppm as shown in Table 1, andfurther resulted in O: 250 wtppm, C: 50 wtppm, N: <10 wtppm, S: <10wtppm, P: <10 wtppm.

Next, the hafnium thus obtained was subject to deoxidation at 1200° C.for 5 hours with molten salt of Ca and CaCl₂. Reduction was realizedwhere O: <10 wtppm and C: <10 wtppm, and other impurities were alsoreduced to 30 wtppm.

Accordingly, it is possible to obtain a high purity hafnium ingot havinga purity level of 4N (99.99 wt %) excluding zirconium.

The sputtering target obtained from this ingot is also capable ofmaintaining high purity, and, by performing sputtering with this target,a uniform high purity hafnium thin film can be formed on a substrate.TABLE 1 wtppm O C N S P Zr Others Raw Material — — — 20 20 5000 800Ingot 250 50 <10 <10 <10 300 70 Deoxidation <10 <10 <10 <10 <10 300 30

Example 2

100 Kg of hafnium metal raw material (zirconium content of 2 wt %) shownin Table 2 was used and dissolved in nitric-hydrofluoric acid. This rawmaterial contained 15000 wtppm, 8000 wtppm and 5000 wtppm of iron,chrome and nickel, respectively, as its main impurities in the rawmaterial.

Next, this hafnium raw material was subject to 10-stage organic solventextraction using a TBP organic solvent, and neutralization treatment wasperformed to obtain hafnium oxide (HfO₂).

Further, this hafnium oxide was subject to chlorination to obtain highpurity hafnium tetrachloride (HfCl₄), and then subject to calciumreduction to obtain a hafnium sponge. This hafnium sponge contained 1500wtppm of zirconium, and the total content of other impurities wasreduced to 1000 wtppm.

Next, the obtained hafnium sponge was used as the raw material, andfurther subject to two-stage melting via hearth melting and ingotmelting with an electron beam to remove volatile elements, gascomponents and so on. As a result of the foregoing process, as shown inTable 2, realized was O: 400 wtppm, C: 30 wtppm, N: <10 wtppm, S: 10wtppm, P: 10 wtppm.

Next, the hafnium thus obtained was subject to deoxidation at 1200° C.for 10 hours with molten salt of Mg and MgCl₂. Reduction was realizedwhere O: 20 wtppm and C: 10 wtppm, and other impurities were alsoreduced to 50 wtppm.

With the sputtering target obtained from this ingot, as with Example 1,a uniform high purity hafnium thin film can be formed on a substrate.TABLE 2 wtppm O C N S P Zr Others Raw Material 10000 5000 4000 100 5020000 30000 Ingot 400 30 <10 10 10 1500 100 Deoxidation 20 10 <10 <10<10 1500 50

Example 3

100 Kg of hafnium oxide (HfO₂) raw material (3N level) shown in Table 3was used and dissolved in nitric-hydrofluoric acid. This raw materialcontained 15000 wtppm, 8000 wtppm and 5000 wtppm of iron, chrome andnickel, respectively, as its main impurities in the raw material.

Next, this hafnium oxide raw material was chlorinated and subject torefining with distillation of 10 or more stages, then further subject tosodium reduction.

Next, the obtained hafnium was used as the raw material, and furthersubject to two-stage melting via hearth melting and ingot melting withan electron beam to remove volatile elements, gas components and so on.As a result of the foregoing process, as shown in Table 3, realized wasZr: 500 wtppm, O: 100 wtppm, C: 100 wtppm, N: 20 wtppm, S: 10 wtppm, P:10 wtppm, others: 30 wtppm.

Next, the hafnium thus obtained was subject to deoxidation at 1250° C.,under argon pressure (4 atm) for 10 hours with molten salt of Ca andCaCl₂. Reduction was realized where 0, C, N, S, P<10 wtppm, and otherimpurities were also reduced to 25 wtppm.

With the sputtering target obtained from this ingot, as with Example 1,a uniform high purity hafnium thin film can be formed on a substrate.TABLE 3 wtppm O C N S P Zr Others Raw Material — 10000 5000 500 10010000 10000 Ingot 100 100 20 10 10 500 30 Deoxidation <10 <10 <10 <10<10 500 25

With respect to the foregoing Examples 1 to 3, results of measuring theresidual resistance ratio are shown in Table 4. As a result, as shown inTable 4, the residual resistance ratio at the ingot stage in Examples 1,2 and 3 is respectively 38, 22 and 45, but respectively increased afterdeoxidation at 200, 120 and 190. Like this, it is evident that hafniumhaving a high residual resistance ratio can be obtained from hafniumhaving ultra high purity. TABLE 4 Hafnium Material Residual ResistanceRatio Example 1 Ingot 38 After Deoxidation 200 Example 2 Ingot 22 AfterDeoxidation 120 Example 3 Ingot 45 After Deoxidation 190 ComparativeIngot 5 Example 1

Comparative Example 1

The raw material shown in Table 2 was subject to plasma arc melting tomanufacture an ingot. The impurity content of the ingot was O: 7,000wtppm, C: 1,800 wtppm, S: 100 wtppm, P: 50 wtppm, Zr: 20,000 wtppm,others: 1,600 wtppm. The residual resistance ratio of this ingot issimilarly shown in Table 4.

As clear from Table 4, since the impurity content is high, the residualresistance ratio was low at 5.

INDUSTRIAL APPLICABILITY

Since the present invention is able to stably manufacture high purityhafnium in which gas components such as oxygen and other impurityelements are reduced by using a hafnium sponge with reduced zirconium asthe raw material and subjecting this hafnium sponge to electron beammelting and deoxidation processing with molten salt, such high purityhafnium can be used as a heat-resistant or corrosion-resistant material,or an electronic material or optical material.

1. High purity hafnium and a target and thin film formed from said highpurity hafnium having a purity of 4N or higher excluding zirconium andgas components, and an oxygen content of 40 wtppm or less.
 2. Highpurity hafnium and a target and thin film formed from said high purityhafnium having a purity of 4N or higher excluding zirconium and gascomponents, and in which the content of sulfur and phosphorus isrespectively 10 wtppm or less.
 3. High purity hafnium and a target andthin film formed from said high purity hafnium according to claim 1having a purity of 4N or higher excluding zirconium and gas components,and in which the content of sulfur and phosphorus is respectively 10wtppm or less.
 4. (canceled)
 5. A manufacturing method of high purityhafnium wherein a hafnium sponge raw material is subject to solventextraction and thereafter dissolved, and the obtained hafnium ingot isfurther subject to deoxidation with molten salt.
 6. A manufacturingmethod of high purity hafnium according to claim 5 wherein, afterperforming deoxidation with molten salt, electron beam melting isfurther performed.